Mailview

Capture outgoing emails during development and view them in a browser UI mounted inside your app.

No Docker. No SMTP server. No external services. Just one line of middleware.
Inspired by Ruby's letter_opener.

Installation

pip install mailview

Quick Start

from fastapi import FastAPI
from mailview import MailviewMiddleware

app = FastAPI()
app.add_middleware(MailviewMiddleware)

That's it. Visit /_mail in your browser to see captured emails.

Features

• Zero config - add middleware, visit /_mail, done
• Persistent storage - emails survive dev server restarts (SQLite in temp dir)
• Full email support - HTML, plaintext, multipart, attachments
• Sandboxed preview - HTML emails render in an iframe without CSS bleed
• Dev-only by default - refuses to activate in production environments
• Self-contained - no external assets, works fully offline

How It Works

Mailview provides drop-in email backends that intercept outgoing emails instead of sending them:

# FastAPI-Mail
from mailview.backend import MailviewBackend
from fastapi_mail import FastMail, ConnectionConfig

config = ConnectionConfig(
    MAIL_BACKEND=MailviewBackend,
    # ... other config
)

# Or with any SMTP-based library, point it at Mailview's capture backend

Captured emails are stored in SQLite at /tmp/mailview/mailview.db and served through the /_mail UI.

Browser UI

Navigate to /_mail to see:

• Inbox - list of captured emails with sender, recipients, subject, timestamp
• HTML preview - rendered email in a sandboxed iframe
• Plaintext - raw text version
• Source - raw email headers and body
• Attachments - download any attached files

Clear all emails with the delete button or DELETE /_mail/api/emails.

Screenshots

Source Tab

Headers Table

Text Tab

Copy Button

Configuration

Mailview works with zero configuration, but you can customise if needed:

app.add_middleware(
    MailviewMiddleware,
    mount_path="/_mail",        # Change the UI path (default: /_mail)
    db_path="/custom/path.db",  # Custom SQLite location (default: /tmp/mailview/mailview.db)
    enabled=True,               # Force enable/disable (default: auto-detect dev environment)
)

Production Safety

Mailview will not activate unless it detects a development environment. It checks for:

• DEBUG=true or DEBUG=1 environment variable
• MAILVIEW_ENABLED=true to explicitly enable
• Framework-specific debug flags (FastAPI's debug=True, etc.)

To be extra safe, don't include mailview in your production dependencies.

Network Binding Warning

Mailview has no authentication. If your dev server binds to 0.0.0.0 (all interfaces) instead of 127.0.0.1 (localhost only), anyone on your local network can access /_mail and view captured emails.

For local development, prefer:

uvicorn app:app --host 127.0.0.1 --port 8000

Framework Support

Requirements

• Python: 3.11+
• Starlette: 0.40.0+
• FastAPI: 0.115.5+ (if using FastAPI)

API Endpoints

The UI is powered by a simple JSON API:

Development

git clone https://github.com/swmcc/mailview.git
cd mailview
make local.install
make local.check

See CONTRIBUTING.md for full development workflow.

License

MIT